The use of adhesives to bond materials to one another is becoming more and more wide-spread and, as a result, it is becoming more and more necessary to learn as much about each individual adhesive system in question when considering which to use for a particular service application. Skilled artisans are constantly searching for new and useful techniques which will enable them to chose one adhesive over another when confronted with a multitude of systems, each of which will apparently do the job.
One of the fields of exploration which has recently become of more concern to the artisan is in the area of stress analysis. The artisan must be able to predict the strength and durability of a particular adhesive system when considering its use. These features of adhesive systems have been very difficult to assess with any degree of particularity because commercially available devices which are designed to accumulate data of this sort have not proven accurate enough, not only from the standpoint of giving false or misleading information but from the standpoint of not being capable of detecting the minute movements involved when test samples are subjected to extraneous forces. Devices now in general use are subject to so many influencing factors that readings obtained therefrom are, in most instances, meaningless. Some of these influencing factors include (1) loading holes off center in producing specimen, (2) glue line voids off center in producing specimen, (3) glue line rotation during exertion of force on specimen, (4) adherend bending rotations of material when force exerted on specimen, (5) adherend tension differential of material during applications of force on specimen (6 ) adherend shear deformation as force is exerted on specimen and the like. Each of these individual occurences are normally manifested during specimen tests and, consequently, each adds its influence to the final information received during the testing program. Other errors are introduced into the calculations by deficiencies inherent in the design of the testing apparatus, e.g., lever systems tend to include "slop" or play in the bearings or pivotal points thereof because lever ends move on arcs rather than in straight lines.
A complete and precise discussion of evaluation techniques and stress analysis for structural bonds under hostile environment can be found in an article in Adhasion, Vol. 18, No. 12, December 1974, published by Bertelsmann Fachzeitschriften GmbH, and continued in Vol. 19, No. 1, January 1975, said article having been authored by the instant inventor.